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QUESTION: Are naturalistic dieting (weight control in the natural environment without formal treatment), exercise, radical weight loss efforts, and binge eating associated with growth in relative weight and onset of obesity in adolescent girls?

Design

Prospective cohort study with 4 years of follow up.

Setting

3 high schools in northern California, USA.

Participants

692 girls (mean age 15 y, 45% white) who were grade 9 students. Girls who were pregnant were excluded.

Main outcome measures

Main results

Analyses were adjusted for baseline BMI and sexual maturation level. Baseline BMI was not related to subsequent growth in relative weight. Baseline incidental exercise, appetite suppressant or laxative use, vomiting for weight control, and binge eating predicted relative weight gain over the 4 year study period (p<0.05). Dietary restraint, self labelled dieting, and exercise for weight control predicted onset of obesity over time. For each unit of increase on the restraint scale, there was a 192% increase in the hazard for onset of obesity (hazard ratio [HR] 2.92, CI 1.74 to 4.89, p<0.001). The hazard for onset of obesity was 324% greater for self labelled dieters than for non-dieters (HR 3.24, CI 1.53 to 6.85, p<0.01), and for each unit increase on the exercise scale, there was a 25% increase in the hazard for onset of obesity over the study period (HR 1.25, CI 1.08 to 1.45, p<0.01).

Commentary

Research on the development of adolescent obesity is limited. This prospective study by Stice et al is one of the few studies that examine the relationship between self employed weight control efforts and weight change and obesity. The findings show that dieting and weight loss efforts predicted increases rather than decreases in relative weight and an increased risk of onset of obesity. The findings have credibility within the context of a rising prevalence of obesity among adult women in the United States despite a dieting prevalence >50%.1

This study is methodologically strong, with analyses controlling for initial BMI and sexual maturity level. The participants were predominantly white and, therefore, the results may not be applicable to ethnic groups with particular vulnerability to obesity. The use of self definition for dieting and the lack of specification of the type and duration of exercise did not allow the researchers to know if participants were actually reducing calories or exercising by standard definitions. Previous studies have shown that people may attribute activities, even those not related to food, as “dieting” activities.2

The results of this study increase our understanding of the potential effects of “generic dieting”, exercise for weight control, and radical weight loss activities on weight and onset of obesity. The notion that such reported activities may be markers for adolescents who may become obese and who may benefit from early intervention is relevant to clinicians. These findings reinforce the need for clinicians to identify adolescents at high risk, assess the meaning of dieting and exercise for weight control, and provide tailored information and interventions to prevent weight gain. The findings of this study are relevant to nurses in the areas of paediatrics, public health, and family, school, and women's health. These clinicians are in a position to initiate obesity risk assessments and primary prevention programmes for adolescents. It is important that these prevention programmes be accompanied by evaluations to assess their effectiveness.

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Copyright 2000 by the RCN Publishing Company and BMJ Publishing Group for Evidence-Based Nursing